This invention relates generally to vacuum insulated containers. More specifically, it relates to improvements in the means for sealing such containers after evacuation and to improvements in the manufacture of such containers.
Vacuum insulated containers variously known as vacuum or thermos bottles or Dewar flasks have been in use for a substantial number of years to provide thermal insulation for various materials desired to be held at or near a particular temperature for prolonged periods of time. Such containers consist of a double-walled receptacle formed of either metal or glass with the space between the walls being evacuated so as to provide the best possible vacuum in that space. Because the vacuum or substantial vacuum in that space is a very poor conductor of heat, there is consequently a minimum of heat loss through the container walls. The performance of such containers is enhanced when the interior surface of the outer wall is coated with a highly reflective material, for instance silver, which retains a very bright reflective surface which does not tarnish or form oxides because of the absence of oxygen in the evacuated space between the walls.
As stated above, such containers may be formed of either metal or glass. Although it is possible that plastics may be used, I am not yet aware of any plastic which is suitable for such purpose when all of the problems, such as desired strength, cost, ease of manufacture and the provision of a truly impermeable wall, are considered. The most commonly used material is glass and the interior surface of the outer wall is commonly coated with silver to provide a reflective surface.
Glass vacuum bottles have been manufactured for a substantial number of years by first positioning a glass tube against the outer wall and by the application of heat bonding that tube to the wall and at the same time piercing a hole through the wall in the area bounded by the tubing. At the completion of these operations a glass tube has been bonded to the wall and encompasses an opening extending into the space between the inner and outer walls. The free end of the tubing is then connected to a vacuum pump which is then operated to evacuate the space between the walls. When the space has been evacuated to the desired degree, the tubing is heated so as to cause it to collapse, closing itself off and thereby seal the now evacuated space between the side walls of the container. The finished product, therefore, consists of the double-walled container with the now sealed glass tubing extending therefrom.
While this structure and method have been successful and continue to be used, there are nevertheless severe disadvantages. One of these disadvantages is that the sealed off tubing extending from the bottle, referred to in the art as the "tubulation", is relatively fragile and when containers of this type are incorporated in devices intended for normal usage means must be provided to protect it. Such means take various forms but usually include a protective cap or cover which encompasses the tubulation and is bonded to the bottle around it. The cap in turn is supported and protected by some kind of resilient or shock absorbing means when the bottle is mounted in a protective jacket to form the so-called vacuum or thermos bottle that is sold for consumer use. The need to provide such protection for the tubulation obviously adds to the cost of manufacture. It in addition requires that the protective jacket be big enough to provide room for it and its protecting means as they may extend from the wall of the bottle as much as three-quarters of an inch.
Another problem with this structure and method occurs during manufacturing. Most commonly, the bottles as described above are manufactured by relatively automatic machinery in which at various stages the operations of flame piercing, tube insertion, tube joining, evacuation and sealing off are performed as a bottle advances from one station to the next. In much of the machinery used for this purpose, a principal support for the bottle being manufactured is provided by the tubulation. It has been found that if the machinery carrying out the described process is operated beyond certain speeds any one bottle in any one position may topple and in doing so fall into adjoining bottles causing them to topple and more than likely breaking, thus causing a production loss with respect to the bottles then in the machine. This imposes an upper limit on the operation of the machine which, as is obvious, precludes optimizing all of the economic benefit to be derived from such automated manufacturing processes.